Floor Insulation Cost UK 2026: Suspended, Solid and DIY Prices

What Kind of Floor Have You Got?

Everything about cost depends on this, and it takes two minutes to find out.

• Suspended timber. Floorboards sitting on joists over an air gap. Typical in homes built from the 1850s to the 1950s, so most Victorian, Edwardian and inter-war houses. The giveaway is air bricks in the outside walls just above ground level. Lift a corner of carpet and you'll see boards, often with gaps between them.
• Solid concrete. Most homes from the 1950s onwards. It feels hard and dead underfoot and there are no air bricks. If your home was built since the early 2000s, the floor was almost certainly insulated when it was built, and there's nothing to do.
• Stone, tile or limecrete laid on earth. Older cottages and period homes. These need specialist advice, especially in a listed building, because the wrong insulation traps moisture in the walls.

Got a cellar you can stand up in? Look up. If you can see joists and the undersides of floorboards, you've got a suspended floor with the easiest access there is.

What It Costs

Fitted prices and the £55 come from the Energy Saving Trust (updated 19 May 2026); its £55 is for Great Britain, and it's £70 in Northern Ireland, where more homes heat with oil. DIY material prices are what Wickes was charging on 11 October 2026: a 170mm loft roll at £27 to £38 for 6.47m2, breather membrane at £74 for 50m2, 100mm Kingspan TP10 at £55 a sheet and P5 chipboard at about £8.50 per m2. The saving is the Energy Saving Trust's, rescaled for your floor size and fuel in the calculator.

What pushes a fitted price up: no access underneath (so the boards come up), fitted kitchens and bathrooms that can't be lifted, pipes and cables in the void, and rotten joists found once you're in there. The last one is worth knowing about anyway.

Is It Worth It?

On the money alone, only in three cases:

• You can do it yourself from below. A cellar or a crawl space you can work in turns a £1,800 job into a £350 one.
• You heat with electric heaters. Heat costs 26.32p a kWh, three times gas, so the same floor saves about £160 a year and even a fitted job pays back in around ten years.
• The boards or screed are coming up anyway. Rewiring, replumbing, a new kitchen, underfloor heating or a damp repair. Then insulation is a small extra on a job you're already paying for, and if you're replacing more than half the floor, building regulations require it (more below).

Outside those, the honest reason to do it is comfort. A cold, draughty floor makes a room feel colder than the thermostat says, and people turn the heating up to compensate. Insulating it fixes that in a way a higher setting never does.

If you've got a gas boiler and a decent floor, put the money into the loft and cavity walls first. They save far more per pound: see our insulation costs guide for every measure side by side.

Start Here: Seal the Gaps (£35, One Afternoon)

On an old suspended floor a lot of the heat loss isn't through the boards. It's cold air blowing up through the gaps between them and under the skirting, straight from the ventilated void. That's the bit you feel on your ankles.

• Gaps between boards: a rubber strip like DraughtEx floorboard gap filler pushes in with the tool it comes with, needs no glue and comes back out if you change your mind. The standard 8mm size fills 3 to 7mm gaps and comes on a 40m roll, which does a typical living room. Measure your widest gap first: there's a thin version for under 3mm and a thick one for 10 to 12mm.
• Under the skirting: a bead of decorator's caulk or flexible sealant along the bottom edge.
• Around pipes coming up through the floor: expanding foam or a pipe collar.

Fill gaps, never the air bricks outside. Those keep the void ventilated so the joists don't rot. Our draught-proofing guide covers doors and windows too.

Insulating a Suspended Floor From Below

If you can get underneath, this is a weekend or two of unpleasant but straightforward work. The aim is a continuous layer between the joists, held up from below, with the void still ventilated underneath it.

1. Check the void first. Look for damp, rot in the joist ends, and anything living down there. Fix any damp before you insulate, or you'll seal the problem in. Make sure every air brick is clear.
2. Lag any water pipes in the void. Once the floor above is insulated the void gets colder, and pipes that never froze before can. Our pipe insulation guide has what to use.
3. Fix a support. Staple breathable membrane or insulation netting to the undersides of the joists, or nail battens along the bottom edges, to carry the insulation.
4. Fit the insulation between the joists. Mineral wool (about 150mm) is cheapest and forgiving of wonky joists. PIR board (about 70mm or more) does more per mm, but has to be cut tight and the edges taped or foamed, or air just goes round it.
5. No gaps. The Energy Saving Trust is blunt that gaps dramatically reduce how well it works. Pack the ends at the walls, and push the wool up against the underside of the boards.
6. Keep cables loose. Electrical cables buried in insulation can overheat. Clip them up out of it, or ask an electrician.

Take photos as you go. The insulation disappears once it's done, and pictures are your evidence for the next Energy Performance Certificate.

No way underneath?

Then the boards have to come up, room by room. Lift every board, fit the insulation as above (on netting slung between the joists), and relay them. It's the same materials with a lot more labour, and you'll break a few boards on the way, so buy some spares. This is where a fitted price goes towards the top of the range.

Insulating a Solid Floor

There are two ways, and neither is a quick job.

• Overlay: lay rigid insulation board over the existing concrete with a membrane, then a floating chipboard deck on top. It raises the floor by about 70mm with a 50mm board, so doors need trimming, skirting and sockets move, and you get a step where it meets the hall or kitchen. Materials run to about £25 per m2.
• Dig out and relay: break up the old slab and pour a new insulated one at the same level. Only sensible during a major renovation.

For most people with a solid floor, a thick underlay and rugs do more for comfort per pound. Save the full job for when the floor's coming up anyway.

Building Regulations

You don't need permission to add insulation to a floor you're not otherwise touching. But in England, if you renovate more than half of a floor (replacing the boards and deck, or the screed), Approved Document L says it should be brought up to a U-value of 0.25 W/m2K, unless that isn't technically possible or wouldn't pay back within 15 years. The same 0.25 applies in Wales and Northern Ireland; Scotland asks for 0.18. In practice that's around 70mm of PIR board or 150mm of mineral wool, depending on the floor.

The legal responsibility is yours as the homeowner, though a decent installer will handle it. If in doubt, ring your local Building Control office before you start.

Grants for Floor Insulation

Floor insulation isn't funded on its own for most people, but it's on the list for the main low-income schemes:

• England: ECO4 (until 31 December 2026, through energy suppliers) and the Warm Homes: Local Grant (through councils), both for lower-income households in less efficient homes.
• Scotland: the Home Energy Scotland Grant and Loan treats underfloor insulation alongside loft and cavity, with a grant of up to £1,500 per improvement.
• Wales: the Warm Homes Nest scheme for lower-income households, and Green Homes Wales interest-free loans for everyone else.

Our grant eligibility checker tells you which you might qualify for, and the grants hub has every scheme by nation.

What You Don't Need

• Anything that blocks the air bricks. Not foam, not tape, not a plant pot. If the void can't breathe, the joists rot, and that's a far bigger bill than any heating saving.
• Multifoil "miracle" insulation instead of proper thickness. The thin foil quilts sold for floors and lofts don't come close to the 0.25 target on their own. Use wool or board.
• Polythene stapled tight under the joists. A sealed plastic sheet traps moisture against the timber. Under the joists you want a breathable membrane or netting.
• Spray foam without asking how it's ventilated. Foam sprayed onto the underside of the boards can work, but ask the installer how the void stays ventilated, whether it can be removed for repairs, and whether a mortgage lender's surveyor will be happy with it.